This invention relates to a device for the repeated reproducible delivery of specific variable amounts by volume of liquid, whereby, between deliveries of repeated reproducible definite amounts by volume of liquid, the total delivery volume of the device can be made accessible for cleaning as becomes necessary without altering the prior adjustment of the definite repeated amount to be delivered. The device can be employed with the advantage for the delivery of very small amounts by volume, e.g., in the microliter or preferably in the nanoliter range. The device can thereby be preferably utilized for the application of small exactly determinable amounts of liquid on to plates for high-performance thin layer chromatography (HPTLC).
In thin layer chromatography, it is conventional to apply small amounts of liquid by the use of syringes or microcapillaries to the thin layer plate. The application of amounts of liquid is thereby possible with sufficient exactitude down to amounts of about 100 nl. (=0.1.mu. l.) Due to the development of high-performance thin layer chromatography (HPTLC), which permits extremely small amounts of substance to be determined quantitatively, the necessity has arisen to apply amounts by volume in the range of 5 to 1000 nl. exactly and reproducibly. For this purpose, a device is known in which the piston of a 1 .mu.l. syringe is connected with a micrometer. By rotation of the micrometer screw, the syringe piston can be moved a precise distance which corresponds to a precise nanoliter amount.
However, this device has several disadvantages. For example, the delivery of the liquid is very slow, since the movement of the syringe piston takes place by rotation of the micrometer screw cut with an extremely fine thread. If identical volumes are to be delivered repeatedly, although in principle it is possible to rotate the micrometer screw each time by the same amount (e.g., from 0.00 to 2.73 mm., then from 2.73 to 5.46 mm., then from 5.46 to 8.19 mm. etc.), apart from the laborious calculation of each successive value (and the possible source of error involved therewith), in this method, not only syringe errors but also micrometer screw errors (variations) are involved. Moreover, a rapid sample change with intermediate rinsing of the syringe is not possible with this device.
Thus, there exists the need for a device which permits definite, preferably very small amounts by volume to be delivered repeatedly and with reproducible exactitude and, between deliveries, which permits the total delivery volume of the syringe for a cleaning or rinsing procedure as it becomes necessary, whereby the once adjusted volume value to be dispensed thereby remains fixed.